Prediction of Creep Curves of High Temperature Alloys using θ -Projection Concept

A computer program based on “MATLAB” was developed to predict creep curves of two high temperature alloys viz. a near α titanium alloy and Fe-Ni-Cr-Al alloy using θ-projection concept. Experimental creep curves generated at 600°C at different stress levels were used. This technique involves fitting of experimental creep curves according to eq εc=εt−ε0=θ1(1−e−θ2t)+θ3(eθ4t−1) to obtain θi parameters for different stress levels. Different θ-values obtained from fitting are then fitted according to eq logθi=ai+biσ+ciT+diσT and experimental strain to fracture values are fitted according to eq logεf=a+bσ+cT+dσT to obtain a set of twenty material constants (ai, bi, ci, dit), and εi), which are further used along with eq εc=εt=ε0=θ1(1−e−θ2t)+θ3(eθ4t−1) to determine four θ-values and fracture strain for each desired combination of stress and temperature in order to generate new creep strain curve. The predicted creep curves for both the alloys have been validated by generating experimental curves. Further, in order to simulate creep behaviour of components of complex geometry such as gas turbine blades and vanes this user defined material model i.e, θ-projection concept has been interfaced with ANSYS. Simulations have been carried-out and validation of the simulation results will be presented in this paper.